The success of a total knee arthroplasty (TKA) may be determined, in part, by the ability of a surgeon to adequately manage (or balance) the soft tissues surrounding the joint. Postoperative malalignment or imbalance of the collateral ligaments can lead to a lax joint and result in early loosening and instability, and leaving the knee too tight may cause stiffness and limited motion. The severity and location of wear patterns on the polyethylene insert are also associated with knee stability from ligament balancing. Establishing a balanced soft tissue envelope remains a challenge that may be not always achieved, and instability, tightness, and wear that result from unbalanced knees may necessitate revision surgery or result in reduced patient satisfaction.
Despite the importance of joint stability to the success of the operation, debate exists regarding how much soft tissue balancing may be appropriate. In general, surgeons believe that the knee should not be too tight and that a little varus-valgus laxity should be achieved postoperatively, with the ideal knee being looser in flexion than in extension, and looser laterally (i.e., under varus stress) than medially, but little evidence supports these beliefs. No available data quantifies a “loose” or “tight” knee. While many surgeons have become skilled in developing a qualitative “feel” for knee laxity or stiffness, an objective definition as to what constitutes acceptable post-operative stability does not exist, and establishing an objective definition for knee stability may be an important step toward improving surgical reconstructions.
Having the ability to accurately and precisely measure intra-operative joint stability represents a key requirement in the process of objectively defining acceptable joint stability and would mark a substantial improvement over the subjective measurements currently made by surgeons.